Retail stores offer goods for sale and need to provide customers with information on item pricing. Price labels typically provide information describing an item the price for that item and a machine-readable code for the item, typically in UPC bar code format. The price of items often changes rapidly, requiring that printed retail labels be manually changed. Items that are on sale often have a larger secondary label, called a shelf-talker, that highlights items on sale for customers. The process of writing and changing retrial pricing is costly, primarily in the labor required to replace tags. Recent art addresses the problem using digital data transmission to electrically changeable retail labels, known as Electronic Shelf Labels (ESL).
U.S. Pat. No. 5,448,226 describes an ESL system having a plurality of electronic price labels (sic) fitted into rails. The rails provide power and communication to each label. Connection to the rail can be provided through direct electrical connection to a conductor in the rail or a radio frequency (RF) interface. The label can be powered though direct electrical connection to power conductors in the rail, a battery or solar cell. Such systems require two sets of patterned conductors and expensive, complex electronic and communication structures.
U.S. Pat. No. 6,186,555 describes paper shelf-talkers that can be attached to conventional paper shelf labels to identify items on sale. Adhesive strips are applied to a perforated substrate that is printed to align text with the adhesive label. Attaching such a shelf-talker to a label requires the assembly to be discarded when pricing is changed. U.S. Pat. No. 5,771,005 describes an auxiliary electronic display that can be attached to an electronic price label (sic) The auxiliary display acts as an electronic shelf talker to identify special prices on goods. Such systems require two sets of patterned conductors and expensive, complex electronic and communication structures.
U.S. Pat. No. 6,130,603 provides a good reference for current Electronic Shelf Labels. Independent modules contain a power supply, antenna and controller. The controller is attached to a conventional liquid crystal display that requires periodic refreshing to maintain an image. Displays in ESLs currently display data on simple seven-segment numeric data. An internal power supply expends about half its power maintaining the display image and the other half of the power maintaining the RF link. Such displays have limited display resolution, and must incorporate expensive and bulky controller and transmission electronics. Such displays further must incorporate a power supply that further increases cost and size.
U.S. Pat. No. 5,751,257 issued May 12, 1998 to Sutherland shows an electronic shelf label having a first and second substrates. Sutherland omits the expensive controller and power portions of the ESL, using a programming device translated across a series of pins and to write segments of an electronic display formed between the two glass substrates. The Southerland apparatus is unreliable, requiring the device to be positioned at a specific initial position and translated specific sequence and rate to update the shelf tag. The amount of information displayed in the Southerland patent is limited to simple numeric data. Such systems omits expensive, complex electronic and communication structures, but require two sets of patterned conductors.
U.S. Pat. No. 3,401,262 issued Sep. 10, 1968 to Fergason et al. discloses a cathode ray tube to apply light to a screen. The screen has a photoconductive layer that is excited by an electrical field applied by fine leads across the photoconductive layer. The screen has a layer of a temperature sensitive cholesteric material that changes reflective wavelength with slight changes in temperature, and changes hue in heated areas. Light from the cathode ray tube strikes the photoconductor layer, creating heat which can be used to selectively change the color of the sheet of cholesteric material. The system uses a complex cathode ray tube and a photoconductor layer and ceases to present an image in the absence of an electrical field.
U.S. Pat. No. 3,578,844 issued May 18, 1971 to Churchill discloses a sheet of gelatin encapsulated cholesteric material without a photosensitive layer. The sheet is put into a first reflective state by heating. Portions of the sheet are written into a black (clear) state by the application of DC fields. The sheet is heated to reset the display. The encapsulated material in the sheet retained written information without fade at ambient conditions for eight weeks. Such systems require two sets of patterned conductors and expensive, complex electronic and communication structures.
U.S. Pat. No. 3,789,225 issued Jan. 29, 1974 to Leder discloses a glassy cholesteric liquid crystal between glass plates. Glassy liquid crystal materials are solidified liquid crystals in an ordered state at ambient temperatures. They are not responsive to electrical fields in the glassy state. The apparatus writes the sheet to an initial state by heating the material above the isotropic (liquid) transition point. As the material is cooled, a high-intensity xenon flash lamp is used to disturb the material so that flash disturbed areas solidify into a state different than areas not receiving flash energy. The imaging system requires that the materials be raised to a high temperature, and cooled at a fast rate in the presence of selective high-intensity flash illumination. No electrical fields are applied to the media.
Conventional, non-glassy liquid crystals have the property of being electrically driven between a planar state reflecting a specific visible wavelength of light and a light scattering focal-conic state at ambient temperatures. Chiral nematic liquid crystals, also known as cholesteric liquid crystals have the capacity of maintaining one of multiple given states in the absence of an electric field. U.S. Pat. No. 5,437,811 issued Aug. 1, 1995 to Doane et al. discloses a light-modulating cell having a polymer dispersed chiral nematic liquid crystal. The chiral nematic liquid crystal has the property of being driven between a planar state reflecting a specific visible wavelength of light and a weakly light scattering focal-conic state. Chiral nematic liquid crystals, also known as cholesteric liquid crystals, have the capacity of maintaining one of multiple given states in the absence of an electric field. The Doane et al. patent discloses the use of only electrical fields to change the optical state of cholesteric liquid crystals. The technology writes image data line sequentially. Sequentially writing data lines is slow compared to writing all pixels at once and requires electrical drivers on each column and row line. Such systems require two sets of patterned conductors and expensive, complex electronic and communication structures.
Displays with pattern of patterned conductors are limited by the resolution of patterning. Fine pitch displays have a high electronic cost due to electronic switching elements on many lines. A typical shelf talker might measure 57 millimeters tall be 100 millimeters high. Typical low cost TN and STN displays are limited to about 3 pixels per millimeter. A shelf talker having a 3 pixel per millimeter pitch would have 473 electrically driven lines. Shelf talkers require finer resolution, preferably 12 pixels per millimeter resolution. That resolution is beyond the technical capacity of low-cost TN and STN displays. A 12 pixels per millimeter shelf talker would have 1880 driven lines, and require finer etching. Electrically driven shelf talkers with the required resolution are economically infeasible.
Light written systems can incorporate a variety of light modulating devices, including transmissive liquid crystal displays, reflective liquid crystal displays or reflective light modulators, such as a Digital Micromirror Device (DMD) from Texas Instruments.
The largest application of DMDs is in digital light projection system, see for example U.S. Pat. No. 6,185,047 issued Feb. 6, 2001 to Peterson et al which discloses the structure of a typical digital light projection system. A short arc (1.3 mm) mercury arc lamp is used as an illumination source. Such lamps provide a continuous energy output. A short arc lamp efficiently produces highly collimated light (good etendu) useful for high-frequency light modulation. Digital light projectors use an elliptical reflector with a cold mirror surface to reflect only visible light. Infrared light, which is a significant portion of the lamp's energy is not processed by such projectors. These types of light projection systems output a small fraction of the total energy produced by a lamp.
Systems using DMDs have operated on non-visible portions of the spectrum. U.S. Pat. No. 5,072,239 is early apparatus which modulated the full output of a tungsten-halogen lamp to provide an image on a xerographic reproduction system. U.S. Pat. No. 6,480,324 operates on the light having wavelengths between 365 and 410 nanometers, which corresponds to near ultra-violet wavelengths. The modulated ultra-violet light is used to optically pattern lithographic resin. Neither of the last two cited patents provides a rewritable image on a media.
There is a need therefore for a low cost rewritable shelf label having high resolution. It is preferable that the image bearing member simple and low-cost, having no connected electrical drive, and having unpatterned electrical conductors.